President Unko is what Sadako Ijūin, an eighteen-year-old third-year student at Shimoshina High School and the president of its student council, is commonly called. She is a tall girl with short blonde hair, orange-yellow eyes, and a short stray lock of hair that stands up from the top of her head, and she usually wears two buttons as barrettes on the left side of her hair. Her given name is properly read as Sadako, but she refuses that reading and insists on being called Unko. The kanji of her name carry a fortunate meaning, roughly that of a lucky child, while the reading Unko happens to be a homophone of the Japanese word for feces. She prefers this unflattering-sounding version because the name Sadako is associated with a famous ghost, and she is terrified of ghosts and ghost stories.

In terms of personality, Unko is cheerful, energetic, and somewhat absent-minded, with an innocent and sparkling manner. Despite the airheaded impression she gives, she is very intelligent and quietly holds the top academic rank in her grade, a contrast between appearance and ability that the story plays for humor. She is also athletic. As student council president, she is one of the three student council officers, together with the vice president and the treasurer, who rescue the protagonist Hime Arikawa from debt collectors by paying off the debt left by his parents. In exchange, the trio makes Hime the council's servant and requires him to spend the rest of his high school life dressed as a girl, and Unko takes part in the council's energetic and often chaotic schemes with a mild and agreeable disposition. Her casual behavior toward other students does not sit well with the school's public morals committee, which criticizes the student council for its lack of respect for rules and authority.

Unko comes from a wealthy family, since her father is the Prime Minister of Japan. The series creator regarded her as one of her favorite characters, describing her as an innocent girl, and had intended to develop the background detail of her father's position in the manga but never got around to it. Because of this, Unko does not undergo significant personal growth in the anime and mostly remains a consistent comedic presence within the trio that controls the protagonist's school life. Her defining traits are her cheerful naivety, her unexpectedly strong intelligence and athleticism, and her unusual insistence on being addressed as Unko, a name that in Japanese doubles as the ordinary word for feces.